aria-expanded="true" is not working on mobile devices

aria-expanded="true" is not working when user closes the dropdown in mobile devices. it it working fine in desktop browser pages.

desktop

<a class="notifLink" data-toggle="dropdown" aria-haspopup="true" id="notificationDropdown" aria-expanded="false" onclick="{!c.readNotifs}">      
                    <h4 class="linkColor">{!v.notifL}</h4>

                </a>

Mobile

<a class="dropdown-toggle notifLink" data-toggle="dropdown" aria-haspopup="true" id="notificationDropdown" aria-expanded="false" onclick="{!c.readNotifs}">
                        <span class="glyphicon glyphicon-bell"></span>
                        <div class="notificationItemsIcon"></div>
                    </a>

what am i missing?